lagar velho - hybridisation

[colin]

All
Recent talk of Lagar Velho prompted me to some thoughts about Neanderderthal - AMH "hybrids". Even those who beleive that Neanderthals were a seperate species, an evolutionary dead-end that became extinct, tend to acknowledge that occassional hybridisation with AMH no doubt occurred, but  they speak of this rather dismissively  as if it were of no consequence. What struck me was that even the occassional hybridisation could have (what was to me at any rate) startling implcations for human lineage. My scenario went thus:

A pair of Neanderthals have an offsping who mates with an AMH, the resulting child going on to mate with another AMH, their coupling resulting in (for the sake of argument) say 6 children, 3 of whom survive to adulthood to produce another 3 surviving children, and so on. The numbers of direct descendants of our original Neanderthal couple rapidly go from 9 to 27 to 81 and on  until after only 12 generations we reach nearly 20,000. After that, of course, the figures rapidly become astronomical. In this process all traces of Neanderthal morphology might well disappear, of course, but I wonder this: given that the pair of Neanderthals in my scenario have thousands of direct descendents a few hundred years later, how can it make any sense to say that they were an evolutionary dead-end and became extinct?

OK, you can argue about the assumptions behind the figures, and sure they would in reality be disrupted by times where maybe whole families died out in harsh winters etc. But what the maths brought home to me  was that even with just  the occassional  "hybridisation" events allowed by Chris Stringer and others - say a handful across Europe in each generation  - over the thousands of years that Neanderthals and AMH apparently co-occupied the continent you would probably arrive at a situation where pretty well everyone  who we would class as AMH would actually be a direct descendent of a Neanderthal couple like the ones in my scenario.
Perhaps all this has been blindingly obvious to many of you all along, but to me it was  something of a revelation.
Any thoughts?
Cheers
Colin

[abazagaroth]

The big problem with the strict OoA2ers, and the genetic studies, is the conclusions they draw regarding behavior. Even assuming that there is no neandertal mtdna in all of the humans alive today, all that really means is that there were AMH surviving and breeding compared to neandertals and those of partial/whole neandertal ancestry.

Simple genetic drift will often lead to the fixation of neutral traits over a long enough period of time assuming a large enough difference in frequencies. But that has little effect on the spread of autosomal traits that can be passed to any offspring in any combination.

[lagarvelho]

All:

It's possible that, if as some people suspect, Neandertals were a rather small population compared to that of AMH, it could well be that population size differentials alone may have been responsible for the lack of mtDNA from Neandertals.  Others, notably Rosalind Harding, have suggested that other kinds of DNA may have originated with Neandertals(at least among some European populations).  I'm not saying that's the case, merely that it has been suggested.
Anne G